noindentfbox{%
    parbox{textwidth}{%
        text
    }%
}

documentclass{article}
usepackage{lipsum}% for example text only
usepackage{hyperref}% for hyperlinked references

usepackage{adjustbox}
usepackage{newfloat}

DeclareFloatingEnvironment[
fileext=loc,
listname={List of cars},
name=Car,
placement=pbth,
within=section,
%chapterlistsgaps=off,
]{car}

begin{document}
section{Bla}
lipsum

begin{adjustbox}{minipage=textwidth-2fboxsep-2fboxrule, fbox, captionbelow={ferrari}, label={car:ferrari}, nofloat=car}
Test
end{adjustbox}

See my new car~ref{car:ferrari}.

lipsum

end{document}